Actually all these critiques of the fediverse are TRUE, these are known challenges, and actually it's not really so bad, but it could be better, and at any rate, Bluesky made a major decision to simplify a lot for new users, and they have. Things seem to just work for people! Incredible!

The thing you often get seen thrown around is "it's amazing, I had no idea a decentralized protocol could just work like that! How on earth did they solve that in a decentralized system and so FAST too!"

It's simple: all those things "just work" because Bluesky is centralized.

Now yes, they are using decentralized techniques. Remember when I said content-addressed storage is a good idea and the fediverse should do it too? IT IS! (And as I also said, it's actually fully possible for the fediverse to do, more on that later.)

But the reality is, it's still *centralized*

In every meaningful way from a power dynamics perspective *EXCEPT* the category of "credible exit" (which I am saying and agreeing is a good idea!) Bluesky is centralized.

MAYBE another big corporation could come along and host all this stuff but that's adding a Bing to our Google

Yes, you can host your own PDS. You can also host your own blog. But try hosting your own PDS and NOT hosting a relay or AppView and you can't do much.

Blogs are decentralized, Google is not.
PDS'es are decentralized, Bluesky is not.

We're getting to the point where we get to why I'm so damn frustrated about this and have been biting my tongue until it nearly comes detached from my mouth: users THINK Bluesky is decentralized because they're TOLD Bluesky is decentralized

AUGH! *That's* what drives me nuts.

Here's an example of this problem in action

fry69: "The working search box was the second thing that impressed me on Bluesky, I thought that was not possible with a decentralized model"

Sorry fry sixty-nine I regret to inform you the reason search works so well is that it's centralized! THAT'S WHY

So hold on, let me set some terms for "decentralization" and "federation" that I think are reasonable.

> Decentralization: the result of a system that diffuses power throughout its structure, so that no node holds particular power at the center.

Pretty reasonable. Do you agree? I hope so!

Okay how about "federation" now because this is a *technical term* that the *fediverse has established* and I'm kinda PO'ed about the goalposts being moved on this one.

A lot of people coming to Bluesky have never heard of "federation" before in a social network so listen up this is important!

Here's my definition of federation:

> Federation: a technical approach to communication architecture which achieves decentralization by many independent nodes cooperating and communicating to be a unified whole, with no node holding more power than the responsibility or communication of its parts.

Now historically, federation has been achieved on the fediverse via "message passing". Actually, this is to the degree where I just always associated message passing with federation, but really, federation is about the distribution of power, creating an abstract whole in a sea of autonomy.

Maybe there is another way to achieve federation, but it's about the power dynamics. It's a technical immersion of power dynamics, the flow and interchange of cooperation between many parts.

So you may say, well, doesn't ATProto have that? After all, messages flow through the different parts!

ActivityPub, as it turns out, follows the actor model of computation. Okay, many people implementing the fediverse don't know about the actor model aspect of ActivityPub but I am here to tell YOU, dear reader, that it is an important thing, not a detail

I'll take one more note about federation which is that often time the message passing mechanism of the fediverse is often called "federation", but theoretically another mechanism could exist, but I'm actually not so sure of that.

There's a reason the actor model and the lambda calculus are undying

Oh god Christine said "the lambda calculus" did you know she's into lisp and functional programming, what's she going to talk about next monads?!?!

I am not going to talk about monads. Not TODAY

But we do need to get a better architectural idea of how these systems work because it matters a lot!

So let me introduce two models of communication which we can use to analyze these two systems. It's important!

- Fediverse/ActivityPub: "message passing"
- Bluesky/ATProto: "shared heap"

Okay, cool, terms established, let's talk about them and why they matter because they matter A LOT

"Message passing" is what ActivityPub uses. It's "like email", people say, and that's true.

Actually it's even a lot like physical mail. You write a letter, you say where it should go, it gets delivered to your house.

Message passing. The world runs on it.

Now I can use message passing to send a message to you *directly* and indeed, that's "like email". For one-to-one correspondence, that's enough.

But it's not enough for a followers/following type mechanism. But we can build it on top! Thank *you* computational abstractions!

On top of "message passing" we will build "publish-subscribe" as a second-layer abstraction

"Your ideas are interesting and I'd like to subscribe to your newsletter."

You send me a letter saying you'd like to hear the things I have to say, okay, you're part of the reader list. That's how it works.

On top of that we can build even more abstractions and the net result is that this is how federation works in pretty much every "federated" system I know.

ActivityPub does some extra work to help you see replies on a thread, think "letters to the editor". This is a bit lossy sometimes though

It's true that sometimes users click over to a thread and see some replies but not all on their instance's UI. There's things that could be done to improve it, but it's sometimes mildly confusing, but not so bad, and you can click over typically to see whatever else is happening, and people learn to

I actually think this is improvable but I mostly don't care because this isn't as big a complaint as people tend to think it is on the fediverse, the other concerns like "what instance do I pick" tend to be bigger and "oh no my server went down"

That can be improved, we'll talk about that later

So okay, the federation is "message passing" and like email, or physical mail. You have an idea how it works.

Now we need to get to that other thing, a "shared heap" architecture. What on earth does that mean?

If "message passing" is like "mail comes to your house", a "shared heap" system works differently

In a "shared heap" system, all the mail gets dumped at the post office, and in the most naive version, you go over there and read through every single piece of mail to see which one is relevant to you

There is no "directed delivery" in a "shared heap" system, which means you are stuck with two things: either a "god's eye view" (Bluesky) or "even lossier about replies than ActivityPub" (Secure Scuttlebutt/Nostr)

The Bluesky approach to the "shared heap" is that *everything* goes into the big, centralized shared heap. Bluesky takes a "god's eye" view: it knows everything, and so knows what all your replies are, and can give you perfect search.

Secure Scuttlebutt / Nostr... well long story. Lossier, I'll say

You can imagine the physical world version of "message passing" already because you already live in this world. Messages come to your house or apartment building or whatever

For Bluesky's "shared heap" architecture, you'd have to build a whole addition to your house for everyone's mail

That's exactly why running a Relay or AppView is expensive: you're building an addition to your house for all the world's mail.

Eeep! That ain't cheap. That's why I'm saying: decentralization also means the ability to *scale down*.

Look, I know that I've been hitting this nail on the head for a while but: the web is open, blogs are open, but Google isn't open

But you could run your own Google, in theory. You could index the web. So why aren't you?

Ah yeah. Same thing here. That's what I mean, that's why it's centralized

Now as I have said, this is a *design decision*. And remember: most users of Bluesky really *don't care*. Decentralization is not their focus, they're trying to get the hell off the nazi hellscape that Musk's toxic reign of Twitter has become.

Bluesky's architecture, actually, is great for them.

If what your *goal* is to get off Twitter, then Bluesky has solved it. They solved it by building another Twitter, and this time it's open source, which is cool! And it might have this "credible exit" thing.

But god damnit it's not decentralized and it's not federated stop TELLING people that

"Oh Christine you're being sensitive"

Maybe, but there are real consequences to this. What if Bluesky/ATProto fails? "Oh well we tried decentralization and that didn't work." If people think something is something that it isn't, then that's a real problem.

Users, clearly, think a lot more of Bluesky is decentralized than it is, and realize less of the consequences than they should. This really worries me. Blocks and DMs are both great examples of this.

Blocking first. Bluesky's decision to have *everything* public means that it is expected that every participating node knows *everything* about who's blocking *everyone*.

"This is consistent with how blocking works on Twitter/X" their paper says

But wait, I'm pretty sure that one's not true though

It is ONE thing to be able to block JK Rowling and for you to see that JK Rowling is blocking you.

It is an ENTIRELY DIFFERENT THING for ANYONE to see who is blocking JK Rowling and who JK Rowling is blocking

This one is shocking to me: this seems like a vector for abusive actors

Now to be completely fair this is something that Bluesky's devs are interested in potentially changing: there is an open issue to discuss the possibility of private blocks https://github.com/bluesky-social/atproto/discussions/1131

What I am saying is there are architectural consequences to fundamental design abstractions

Yes, I may sometimes seem silly over here, SICP-hugging fangirl, come on we're just trying to build things that *work* over here

Look I'm a lisp lady, I know the realities of "Worse Is Better" more than most, I now the right CS designs don't win

But Conway's Law flows in two directions!

You know what, we'll come back to "bidirectional Conway's Law", let's talk about Direct Messages for a minute because I think those are telling

Direct Messages in Bluesky, wait how do they work if ATProto is public?

Did you guess?

DMs are centralized! All DMs flow through Bluesky